Reciprocating compressor and method of lubricating the reciprocating compressor

ABSTRACT

In a reciprocating compressor, an adequate lubricating effect is ensured for a sliding surface between a piston and a cylinder bore, and the leakage of a refrigerant for discharge is prevented. 
     After a lubricating oil mixed within the refrigerant is separated by an oil separator  23  on a discharge side, the separated lubricating oil is guided via an oil supply hole  29  in a cylinder block  1  to the sliding surface between the cylinder bore  12  and the piston  13  that reciprocates within the cylinder bore  12  thereof in order to lubricate the surface. In this reciprocating compressor, the intermediate axial portion of the outer circumference of the piston  13  has a small diameter in order to define an oil sump  30.  The oil sump  30  is configured so as not to directly communicate with a drive chamber  7,  and oil always collects within the oil sump  30.

TECHNICAL FIELD

The invention relates to a reciprocating compressor in which a pistonreciprocates within a cylinder bore and specifically relates to atechnique for lubricating the sliding surface between the cylinder boreand the piston.

PRIOR ART

In reciprocating compressors, an oil separator is provided on thedownstream side of a discharge chamber, and after a refrigerant gas isseparated from a lubricating oil by the oil separator, the lubricatingoil is directed to and lubricates a sliding surface between a piston anda cylinder bore due to the pressure differential between the suction anddischarge sides and is then returned to a drive chamber on thelow-pressure side.

In order to improve the effect of lubricating the sliding surfacebetween the piston and cylinder bore, the compressor has an oil grooveextending axially toward the outer circumference of the piston. In aknown configuration, the lubricating oil is supplied from an oil holeand is guided to the sliding surface via the oil groove, which activelycommunicates with the drive chamber. This lubricating technique isdisclosed, for example, in Japanese Laid-open Patent Publication No.10-141227.

However, in systems in which the lubricating oil is separated from therefrigerant gas at the sliding surface between the piston and thecylinder bore due to the pressure differential between the suction anddischarge sides, the use of a configuration comprising the oil groove onthe outer circumference of the piston creates the problems of leakage ofthe refrigerant into the drive chamber via the oil groove and a decreasein performance due to the active communication of the oil groove withthe drive chamber. This phenomenon is particularly problematic incompressors that employ carbon dioxide (CO₂) as a refrigerant due to thelarge pressure differential between the suction and discharge pressures.

The invention has been designed with due consideration given to theseconventional problems and has objectives to facilitate an adequatelubricating effect for the sliding surface between the piston and thecylinder bore of a reciprocating compressor and to prevent leakage ofthe refrigerant.

DISCLOSURE OF THE INVENTION

In order to attain the above objectives according to the invention, anoil sump is provided on the sliding surface between the piston and thecylinder bore in a reciprocating compressor. As a result, thelubricating oil collects in the oil sump, the lubricating oil ensures anadequate lubricating effect for the sliding surface, and seizure isprevented. Moreover, a configuration is taught in which the oil sumpdoes not communicate with the drive chamber, which is situated on thelow-pressure side, so that connection essentially occurs only via thegap between the piston and the cylinder bore. This enables the amount ofrefrigerant that leaks toward the drive chamber side to be reduced andprevents a drop in performance.

Consequently, lubricating oil directed toward the oil sump is preferablya lubricating oil separated from the refrigerant for discharge, and aconfiguration in which the lubricating oil is directed due to thepressure differential between the suction and discharge sides ispreferable. This construction is particularly effective to reduce theamount of leaking refrigerant when utilized with a compressor that usescarbon dioxide as the refrigerant.

It is also preferable to locate the oil sump around the entirecircumference of the sliding surface. In this case, the entirecircumference of the sliding surface is sealed and the lubricating oilcollects in the oil sump, which further reduces the amount ofrefrigerant that leaks toward the drive chamber.

It is also preferable to dispose the oil sump on the outer circumferenceof the piston. For this configuration, the intermediate axial portion ofthe outer circumference of the piston preferably has a small diameter.By disposing the oil sump on the piston, the oil sump can bemanufactured using the most commonly known outer circumferenceprocessing methods in machine tooling and as a result, the associatedprocessing is easily performed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section showing the reciprocating compressor of thefollowing embodiment.

FIG. 2 is an expanded view of Area A in FIG. 1.

FIG. 3 is a descriptive diagram showing a modified example of the oilsump.

FIG. 4 is a descriptive diagram showing another modified example of theoil sump.

FIG. 5 is a descriptive diagram showing yet another modified example ofthe oil sump.

EMBODIMENT OF THE INVENTION

Hereinafter, an embodiment of the invention shall be described withreference to the drawings. This embodiment, as is shown in FIG. 1, is anapplication for a cam-plate-type reciprocating compressor. A fronthousing 2 is joined to the front end of a cylinder block 1, therebyforming part of the outer edge of the compressor, and a rear housing 5defining a suction chamber 3 and a discharge chamber 4 is joined to therear end thereof via a valve plate 6.

A drive shaft 8 is connected to a source of power and penetrates througha drive chamber 7 formed in the front housing 2, and the drive shaft 8is rotatably supported by the cylinder block 1 and the front housing 2via radial bearings 9 and 10. A rotational cam plate 11 is containedwithin the drive chamber 7 and the rotational cam plate 11 is anchoredto the drive shaft 8.

The cylinder block 1 comprises a plurality of cylinder bores 12penetratingly and circumferentially disposed and regularly spaced, andpistons 13 are slidably disposed within the cylinder bores 12. The baseends of the pistons 13 extend into the drive chamber 7 and are coupledto the rotational cam plate 11 via a shoe 14.

Therefore, when the drive shaft 8 is rotated, the rotational movementthereof is converted into linear reciprocating movement of the pistons13 by the rotational cam plate 11 and the shoe 14. Due to thereciprocating movement of the pistons 13 within the cylinder bores 12, arefrigerant in the suction chamber 3 is drawn into the cylinder bores 12via a suction valve (not shown) and then, while being compressed, isdischarged toward the discharge chamber 4 via a discharge valve 15. Theupper half of FIG. 1 shows one of the pistons 13 at its top dead pointand the lower half of the drawing shows another one of the pistons 13 atits bottom dead point.

The radial bearing 10 is disposed within a circular hole that isprovided in the central portion of the cylinder block 1. A thrust race16 and a plate spring 17, which urges the rear portion of the driveshaft 8 forward, are disposed on the bottom of the hole. The urgingforce of the plate spring is supported by a thrust bearing 18 disposedbetween the rotational cam plate 11 and the front housing 2.

A chamber 19 is hollowed out in the central portion of the cylinderblock 1 and opposes the valve plate 6. The chamber 19 is communicatedwith the discharge chamber 4 by a first discharge pathway 20 near themid-section in the vertical direction and communicates with an externalcircuit, which is a refrigeration circuit, via a second dischargepathway 21 on the upper side. A fixture 22 for affixing the dischargevalve 15 to the valve plate 6 is penetratingly located in the firstdischarge pathway 20.

A centrifugal-separation-type oil separator 23 for separating thelubricating oil from a highly pressurized refrigerant gas sent throughthe chamber 19 to the refrigeration circuit is provided within thechamber 19. The oil separator 23 comprises a base 25 with a separationchamber 24 having a bottomed, circular hole shape and a gas duct with aflange 26 attached to the base 25 so as to hang concentrically from theedge of the upper opening of the separation chamber 24. The separationchamber 24 communicates with the first discharge pathway 20 via a hole27 that penetrates a side wall of the base 25. The hole 27 opens almosttangentially to the inside of the separation chamber 24.

Therefore, the lubricating oil is introduced into the separation chamber24 with the refrigerant so that it travels from the first dischargepathway 20 through the hole 27 to rotate along the periphery of the gasduct 26, the lubricating oil then collides against the circumferentialwall of the separation chamber 24 due to centrifugal force, separatesfrom the refrigerant and flows downward, passes through a penetratinghole 28 located in the bottom wall of the oil separation chamber 24, andcollects at the bottom of the chamber 19.

The refrigerant for discharge that is separated from the lubricatingoil, on the other hand, is sent to the refrigeration circuit from thegas duct 26 via the second discharge pathway 21.

An oil supply hole 29 is provided in the cylinder block 1 in order toguide the lubricating oil that has collected in the chamber 19 to thesliding surface between the pistons 13 and the cylinder bores 12. Theoil supply hole 29, on one end, is communicated with the bottom surfaceof the chamber 19, and on the other end, with an oil sump 30 disposed onthe sliding surface between the pistons 13 and the cylinder bores 12.

In this embodiment, the oil sump 30 is formed by providing asmall-diameter portion on the intermediate axial portion of the outercircumference of the pistons 13. In other words, by utilizing on thepiston 13 a portion having a diameter less than the outer diameters ofthe head of the piston 13 opposing the cylinder bores and the base ofthe piston 13 facing the drive chamber 7, a ring-shaped oil sump 30 isdefined.

The oil sump 30, as is shown in FIG. 1, always communicates via the oilsupply hole 29 with the chamber 19, which is on the discharge side, butdoes not communicate with the drive chamber 7 on the low-pressure sideduring the entire stroke of the reciprocating pistons 13. In otherwords, each oil sump 30 communicates with the oil supply hole 29 at thebase and head ends of the pistons 13 even when the pistons 13 arelocated at the top or bottom dead points while not communicating withthe drive chamber 7 even when the pistons 13 are located at the bottomdead point. Each oil sump 30, as shown in FIG. 2, is configured so as tocommunicate with the drive chamber 7 via the smallest clearance C(hereinafter referred to as a “side clearance”) that is necessary toensure the proper sliding action of the pistons 13 against the cylinderbores 12. The head of each piston 13 includes a piston spring 13 a.

In the compressor of this embodiment, which is configured in the mannerdiscussed above, when the pistons 13, which are coupled to therotational cam plate 11 that rotates in conjunction with the drive shaft8, reciprocate linearly within the cylinder bores 12 and compressionbegins, the compressed refrigerant gas pushes open the discharge valve15, is discharged into the discharge chamber 4, and is then introducedinto the chamber 19 from the first discharge pathway 20. The lubricatingoil in the refrigerant gas introduced into the chamber 19 in conjunctionwith rotation is separated from the refrigerant gas due to centrifugalforce, flows down the wall surface of the separation chamber 24 underits own weight, and from the penetrating hole 28 collects at the bottomof the chamber 19.

In this manner, the lubricating oil separated from the refrigerant gasthat collects at the bottom of the chamber 19 is sent through the oilsupply hole 29 to and collects in the oil sumps 30 on the outercircumferences of the pistons 13. The lubricating oil is supplied to thesliding surface by the reciprocating motion of the pistons 13 in orderto lubricate the sliding surface. Therefore, the sliding surface isreliably lubricated and seizure is prevented.

The oil sumps 30 do not directly communicate with the drive chamber 7,which is located on the low-pressure side, but rather communicate viathe side clearances C, so that a sealing effect due to the lubricatingoil collecting in the oil sumps 30 is attained, and leakage of therefrigerant gas from the side clearances C is prevented. As a result,the amount of refrigerant that leaks to the drive chamber 7 is reduced.In this embodiment, the oil sumps 30 are located around the entirecircumference of the sliding surfaces, so that a drop in performanceattributable to the leakage of the refrigerant is prevented.

This design is even more effective when utilized with a compressor thatguides the oil under extremely high pressure, such as a compressor thatemploys carbon dioxide (CO₂) as the refrigerant.

In this embodiment as well, a small diameter portion formed in theintermediate axial portion of the outer circumferences of the pistons 13defines a ring-like oil sump 30, so that the oil sump 30 can beprocessed using the most commonly utilized outer circumference cuttingmethods in machine tooling, whereby the associated production is easilyperformed. By providing the oil sumps 30 in this embodiment, the area ofthe sliding surface between the pistons 13 and the cylinder bores 12 canbe reduced, so that sliding resistance is reduced, and loss of power isdecreased.

The invention is not limited to the above embodiment and may beappropriately modified within a range that does not diverge from itsfundamental nature. For example, although the oil sumps 30 were definedby providing a small diameter portion on the outer circumference of thepistons 13, the oil sumps 30 can also be defined by forming a ring-likerecess on the inner surface of the cylinder bores 12 as shown in FIG. 3.In the alternative, the oil sumps 30 can be defined on both the pistons13 and the cylinder bores 12.

The shape of the oil sumps 30 is not required to be limited to aring-like shape. As shown in FIG. 4, for example, the shape can bemodified to a substantially spline configuration with a plurality ofaxially extending, linear grooves 30 a that are circumferentiallydisposed. In the alternative, a plurality of ring-like grooves 30 b canbe axially formed in parallel to each other on the outer circumferenceof each piston 13, as shown in FIG. 5. The linear grooves 30 a and thering-like grooves 30 b in the configurations shown in FIGS. 4 and 5 mustbe mutually communicated by a connecting pathway to neighboring grooves.

Furthermore, the oil sumps 30 are not required to be defined around theentire circumference and may instead cover only a portion of thecircumference. It goes without saying that these techniques can also beapplied to a non-cam-plate-type compressor, as long as it is areciprocating compressor. Moreover, the oil separator 23 is not limitedto one that uses a centrifugal separation method as the use of anotherseparation technique would not hinder the invention.

Industrial Applicability

As has been discussed above, the invention ensures reliable lubricationfor the sliding surface between the pistons and cylinder bores, preventsburning, and prevents a drop in performance attributable to leakage ofthe refrigerant for discharge from the sliding surface.

What is claimed is:
 1. A reciprocating compressor comprising a cylinderbore and a piston that reciprocates within the cylinder bore and guidesa lubricating oil to a sliding surface between the cylinder bore and thepiston in order to lubricate the sliding surface, wherein an oil sump isdefined on the sliding surface at which the lubricating oil collects anddoes not communicate with a drive chamber to which a base of the pistonfaces, and wherein the lubricating oil is guided to the oil sump due toa pressure difference between a suction side and a discharge side.
 2. Areciprocating compressor comprising a cylinder bore and a piston thatreciprocates within the cylinder bore and guides a lubricating oil to asliding surface between the cylinder bore and the piston in order tolubricate the sliding surface, wherein an oil sump is defined on thesliding surface at which the lubricating oil collects and does notcommunicate with a drive chamber to which a base of the piston faces,and wherein the lubricating oil is separated from a refrigerant and isguided to the oil sump due to a pressure difference between a suctionside and a discharge side.
 3. The reciprocating compressor according toclaim 2, wherein the refrigerant is carbon dioxide.
 4. The reciprocatingcompressor according to claim 1, wherein the oil sump is defined aroundthe entire circumference of the sliding surface.
 5. The reciprocatingcompressor according to claim 1, wherein the oil sump is defined on theouter circumference of the piston.
 6. The reciprocating compressoraccording to claim 5, wherein the oil sump is defined on an intermediateaxial portion of the outer circumference of the piston that is formed tohave a small diameter.
 7. A reciprocating compressor comprising acylinder bore and a piston that compresses a refrigerant drawn from asuction chamber due to reciprocating movement of the piston within thecylinder bore and discharges the refrigerant to a discharge chamber,wherein the piston guides a lubricating oil, which is separated from therefrigerant gas after discharge, to a sliding surface between thecylinder bore and the piston due to a pressure differential between asuction side and a discharge side, the reciprocating compressor furthercomprising an oil sump defined on the sliding surface, wherein the oilsump is defined at an intermediate axial zone on the outer circumferenceof the piston having a diameter that is smaller than both opposing sidesof the intermediate axial zone, wherein the oil sump always communicateswith the discharge side, which is the supply side of the lubricatingoil, during the entire stroke of the reciprocating piston, and the oilsump does not communicate with a drive chamber that is the outflow sideof the lubricating oil, the drive chamber accommodating a cam plate fordriving the piston.
 8. A method for lubricating a reciprocatingcompressor that comprises a cylinder bore and a piston that reciprocateswithin the cylinder bore that guides a lubricating oil to a slidingsurface between the cylinder bore and the piston in order to lubricatethe sliding surface, the method comprising guiding the lubricating oilto an oil sump defined on the sliding surface due to a pressuredifference between a suction side and a discharge side, collecting thelubricating oil in the oil sump, and supplying the lubricating oil fromthe oil sump to the sliding surface without causing the oil sump tocommunicate with a drive chamber to which a base of the piston faceswhile reciprocating the piston.
 9. A method for lubricating areciprocating compressor that comprises a cylinder bore and a pistonthat reciprocates within the cylinder bore that guides a lubricating oilto a sliding surface between the cylinder bore and the piston in orderto lubricate the sliding surface, the method comprising guiding thelubricating oil, which has been separated from a refrigerant, to an oilsump defined on the sliding surface due to a pressure difference betweena suction side and a discharge side, collecting the lubrication oil inthe oil sump and supplying the lubricating oil from the oil sump to thesliding surface without causing the oil sump to communicate with a drivechamber to which base of the piston faces while reciprocating thepiston.